simple test builds via GitHub Action

.github/workflows/build.yml

@@ -0,0 +1,41 @@
+name: Build Hugo
+
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+      with:
+        fetch-depth: 1
+        lfs: false
+    - uses: actions/setup-node@v1
+      with:
+        node-version: "12.x"
+    # https://github.com/actions/cache/blob/master/examples.md#node---yarn
+    # https://github.com/actions/cache/issues/60
+    - name: Get yarn cache location
+      id: yarn-cache
+      run: echo "::set-output name=dir::$(yarn cache dir)"
+    - name: Cache dependencies
+      uses: actions/cache@v1
+      with:
+        path: ${{ steps.yarn-cache.outputs.dir }}
+        key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-yarn-
+    - run: yarn install --no-ignore-optional --frozen-lockfile
+    - run: yarn hugo:version
+    - run: yarn build:preview
+    - uses: actions/upload-artifact@master
+      if: github.event_name == 'pull_request'
+      with:
+        name: public
+        path: './public'